1. Field of the Invention.
This invention is concerned with a method for forecasting engine failure from particle size distribution of metal contaminant contained in the lubricant used in said engine.
2. Description of the Prior Art.
Wear at the interface between moving parts is a normal characteristic of machine operation. The kind and the rate of wear depend on the machine. Lubrication is normally provided between moving surfaces to minimize the wear. During operation millions of minute wear particles enter the lubricating oil. The particles range in size from several microns to a small fraction of micron, for example 20 millimicrons.
It has long been recognized that a knowledge of the quantity and of the rate of increase in the quantity of foreign material, particularly iron, in the lubricating oil of an engine can give valuable insight into the condition of the engine. Because the quantity of such material is extremely small, for example a few parts per million in the oil of a typical engine in good condition, it has been necessary to resort to sophisticated techniques to analyze the lubricating oil.
If oil containing these particles is observed under a high-powered transmitted-light microscope, only the largest particles can be seen. Nor is the situation improved by resorting to a microscope employing phase contrast or other interference techniques. The basic problem is that most of the particles range in size from a wavelength to a small fraction of a wavelength of light, and they do not disturb the phase or amplitude of the lightwave sufficiently to be seen.
Spectrographic techniques have been used relatively extensively to analyze lubricating oil, but even these techniques do not provide as much information as might be desired. For example, a spectrographic analysis is unable to distinguish between two samples containing foreign particles of very different average size but having the same total parts per million of contaminant.
The highly-stressed wearing parts of a machine are usually made of steel. Therefore, if the ferrous particles which collect in the oil are separated and examined, very significant information about the condition of the machine is capable of being obtained.
Heretofore, special magnetic techniques have been used which permit particles of iron or other magnetic material to be precipitated from an oil sample. In such system, the oil flows along a substrate in a magnetic field and large particles are deposited on one end of the substrate and small particles on the other. Particle sizes grade continuously in between. The substrate with the deposited particles affords a means of determining the condition of the engine and of predicting incipient failure.
The above described system, while effective, is time-consuming, expensive and, in some aspects, cumbersome. Thus, in addition to the special magnetic equipment requisite for carrying out the particle size distribution analyses, it is necessary, after the sample has been pumped through the system, to effect a washing and fixing cycle during which the oil remaining on the slide is removed and the particles are caused to adhere to the substrate.